Plasticizers have been used for decades for the processing of plastics such as Polyvinyl chloride (PVC). Plasticizers are additives which are used in polymer processing and which improve processability, flexibility and extensibility. The plasticizers for producing flexible PVC are mainly phthalic esters, such as the all-purpose products di-2-ethylhexyl phthalate (DEHP), diisononyl phthalate (DINP) and diisodecyl phthalate (DIDP). Rapid-gelling plasticizers, such as the short-chain phthalates dibutyl phthalate (DBP), diisobutyl phthalate (DiBP) and benzyl-n-butyl phthalate (BBP) can be added in order to improve the speed of the processes or to reduce the amount of energy that they consume.
The use of phthalates generally, and in particular the use of the rapid-gelling phthalates based on alcohols with a carbon chain length of from 3 to 6, with no branching, is subject to continuously increasing restriction deriving from legal requirements. According to EU Directive 2005/84/EC, it is no longer permissible to use concentrations greater than 0.1% of the plasticizers diisononyl phthalate (DINP), diisodecyl phthalate (DIDP) and di-n-octyl phthalate (DnOP) to produce toys and baby products which could be placed in children's mouths. The use of concentrations greater than 0.1% of di-2-ethylhexyl phthalate (DEHP), dibutyl phthalate (DBP) and benzyl butyl phthalate (BBP) in toys and baby products is forbidden. The phthalates dibutyl phthalate (DBP), diisobutyl phthalate (DiBP), benzyl butyl phthalate (BBP) and di(2-ethylhexyl) phthalate (DEHP) have been added to the list of candidates for classification as substances of very high concern (SVHC) by the European Chemicals Agency (ECHA).
With respect to the abovementioned rapid gelling, there is a need for a phthalate-free replacement material for the rapid-gelling phthalates and in particular for the blends of these with all-purpose plasticizers.
EP 1 983 024 A1 proposes benzyl alkyl trimellitates as rapid-gelling ester mixtures. The ester mixtures were obtained directly in a one-pot reaction. No study of the individual components was carried out; no particular advantages of the mixture over the individual components have been described.
EP 2 039 718 A2 describes rapid-gelling plasticizer mixtures based on aryl alkylsulphonate and on diol dibenzoates. The particular property of these plasticizer mixtures is low volatility. According to the examples, addition of the rapid-gelling diol dibenzoates to the aryl alkylsulphonate leads to more rapid gelling than the aryl alkylsulphonate alone; the gel time achieved was not shorter than that of the individual components, i.e. the diol dibenzoate in this case.
EP 2 145 914 A1 describes the improvement of gelling properties of plasticizers through addition of triacetin.
WO 2006077131 A1 describes C9- to C10-alkyl benzoates as low-volatility viscosity reducers in PVC plastisols with standard plasticizers. Addition of the more rapid-gelling alkyl benzoates is described as giving a generally expected reduction in the solvation temperature of the standard plastisol formulation; there is no description of any significant reduction to a value below the results from the individual components.
WO 97/39060 A1 suggests the use of alkyl benzoates as processing aids in PVC pastes with standard plasticizers, and it is emphasized here that the alkyl benzoates do not have any material effect on the gelling properties.
The patents EP 1 415 978 A1 and EP 1 354 867 A2 propose the use of mixtures of isomeric decyl benzoates and of isomeric nonyl benzoates with dialkyl phthalate, dialkyl adipate or cyclohexanedicarboxylic ester, but no rapid gelling behaviour of the mixtures beyond that of the individual components was discovered.
WO 2009085453 A2 recommends rapid-gelling non-phthalate plasticizers for accelerating processing when using the slow-gelling cyclohexanecarboxylic esters, with the expected result of an appropriate acceleration.
Mixtures of benzoic esters have been known for a long time. In DE 1 962 500 A1, mixtures based on alkyl benzoate with succinic diesters exhibit excellent values for resistance to staining in the final flexible-PVC product.
However, the compositions described in the prior art do not satisfactorily meet the requirement for rapid processing and/or reduced energy consumption in processing.
The object of the present invention therefore consisted in finding novel phthalate-free plasticizer formulations with good gelling properties for plastics, in particular PVC, where these permit rapid processing and/or reduced energy consumption in processing.
Surprisingly, it has now been found that phthalate-free plasticizer preparations of a mixture of at least one aryl alkylsulphonate and of at least one ester of benzoic acid with monohydric C9- and C10-alcohols gel unexpectedly rapidly and have smaller gel times than the two individual components alone, and have smaller gel times than would be expected on the basis of a linear relationship involving the individual components.